Common Heat Treatment Methods for Metal Materials
1. Annealing Process:
Heat the steel to a temperature of Ac3 + 30–50°C, Ac1 + 30-50°C, or below Ac1 (refer to relevant reference materials for specific temperatures).
Typically, allow the steel to cool slowly within the furnace.
2. Normalizing Process:
Heat the steel to Ac3 or Accm + 30–50°C, hold the temperature for a specified period, and then cool it at a rate slightly faster than annealing.
3. Quenching Process:
Heat the steel to a temperature above the phase transition point (Ac3 or Ac1), maintain the temperature for a specified time, and then cool it rapidly in water, nitrate salt solution, oil, or air.
Purpose: Quenching is typically used to achieve a high-hardness martensitic structure. For some high-alloy steels (e.g., stainless steel or wear-resistant steel), quenching is aimed at obtaining a uniform austenitic structure, which enhances wear resistance and corrosion resistance.
4. Tempering Process:
Reheat the quenched steel to a temperature below Ac1, hold it at the temperature for a specified time, and then cool it in air, oil, hot water, or water.
5. Quenching and Tempering Process:
Quenching followed by high-temperature tempering is referred to as quenching and tempering.
Heat the steel to a temperature 10-20°C higher than the quenching temperature, hold it, perform quenching, and then temper at a temperature between 400–720°C.
Additional Heat Treatment Methods for Metal Materials
6. Aging Process:
Heat the steel to 80–200°C, hold it for 5–20 hours or longer, and then remove it from the furnace to cool in air.
Purpose:
Stabilize the quenched structure of the steel, reducing deformation during storage or use.
Relieve internal stresses caused by quenching and grinding, thereby stabilizing shape and dimensions.
7. Cryogenic Treatment Process:
Cool the quenched steel in a low-temperature medium (such as dry ice or liquid nitrogen) to –60 to –80°C or lower.
After the temperature becomes uniform, remove the steel and allow it to warm gradually to room temperature.
8. Flame Hardening Process:
Use a flame produced by the combustion of an oxygen-acetylene gas mixture to rapidly heat the surface of the steel.
Once the quenching temperature is reached, immediately cool the surface with water.
9. Induction Hardening Process:
Place the steel in an inductor to generate an induced current on its surface, rapidly heating it to the quenching temperature within a short period.
Cool immediately with water.
10. Carburizing Process:
Place the steel in a carburizing medium, heat it to 900-950°C, and hold it to allow the surface to develop a carburized layer with the desired carbon concentration and depth.
11. Nitriding Process:
Use active nitrogen atoms released from ammonia decomposition at 500–600°C to saturate the surface of the steel, forming a nitrided layer.
12. Carbonitriding Process:
Simultaneously introduce carbon and nitrogen into the surface of the steel.
Purpose: Enhance the surface hardness, wear resistance, fatigue strength, and corrosion resistance of the steel.
